In a study published in the Archives of Internal Medicine, researchers report that repeated job losses may be as damaging to the heart health as smoking, high blood pressure, or diabetes.

Among Americans aged 50 to 75, the unemployed suffer heart attacks at a rate that is 35% higher than that among employed people with otherwise similar risk factors, and the rate seems to rise with every new period of unemployment.

The team of researchers from Duke University analyzed data on more than 13,000 middle-aged and older adults who agreed to biennial interviews about their work and health status.

The study is not the first to connect employment status and heart attack risk, but unlike most previous research on the topic, it follows participants over many years — in this case, 18 years. That gave the team a rare opportunity to clarify the effects of multiple periods of unemployment, to see if the effect of job loss of the heart is cumulative.

The answer, apparently, is yes. After the first job loss, the increased risk of heart attack during the study period among the unemployed was around 22% compared to those still working, but that risk increased to 63% after four or more bouts of joblessness.

"The (magnitude) of the impact was striking to us," says Dr. Eric Peterson, a cardiologist at Duke and the senior author on the study. "There is this compounded effect of multiple job losses on an individual's health. I think that was interesting and unique to see."

Peterson and his co-authors used data from the U.S. Health and Retirement Study that was conducted between 1990 and 2010, a period that spanned both economic boom years and recessions. In addition to questions about their occupational status and heart health, the study participants were asked about their age, sex, race or ethnicity, educational background, and a whole host of health behaviors, such as smoking and exercise patterns, and health conditions like hypertension or diabetes.

Even after adjusting for these factors, all of which are known to influence heart attack risk, Peterson and his colleagues found that unemployment remained strongly associated with higher heart attack rates. And while the effect is generally biggest in the first year after a job loss, that excess risk does not go away entirely once a person returns to work.

The more times a person loses a job during his or her career, it seems, the higher the risk of heart attack. In fact, the difference between a person who has never lost his job and someone who has been unemployed four or more times is as big as the difference between a nonsmoker and a smoker, or between a non-diabetic and a diabetic, when it comes to heart problems.

What remains unclear, however, is what factors are contributing to the increased heart risk. Stress is certainly a factor, but the cumulative effect of unemployment suggests something more complicated may be contributing to the trend. No one thinks it's pleasant to get fired or laid off. But, as the authors of an editorial accompanying the research say, the precise mechanism linking joblessness to heart attacks remains unknown.

For his part, Peterson believes there may be several possible explanations. If laid-off workers lose their health insurance, they may neglect treatment of existing conditions, like hypertension or high cholesterol, or fail to get diagnosed and treated when new issues crop up, making them more vulnerable to events like a heart attack.

Budget constraints may also lead people to give up on healthy foods and hobbies, like a gym membership, that protect the heart but may seem too expensive to justify.

Then there's the stress from a job loss. People who lose their livelihoods certainly feel anxious, worried, worthless, or even lonely. They may alter their behaviors as a result: eating worse, smoking more, or drinking more, for example.

Most intriguing of all, however, and by far the least understood, are the role that stress hormones may play. They appear to have a direct impact on cardiovascular health, causing blood pressure and blood sugars to rise, at least in the short term. Researchers are still uncovering how those hormones might affect cardiovascular risk in the long-term.

Until more definitive studies expose exactly how joblessness is affecting the heart, Peterson hopes his research will prompt doctors and researchers to start considering the substantial impact of their patients' financial health on physical health, and motivate them to think about possible interventions. Could counseling, perhaps, help to mitigate the cardiovascular risk that comes with job loss?

The present study wasn't designed to answer that question, but it does hint that some heart attack risk may be caused by the financial and emotional strains of dealing with an unintentional job loss, which can be mitigated with interventions such as counseling or stress reduction programs. With heightened awareness of how harmful unemployment can be on the heart, guiding those who are out of jobs to helpful interventions may help them avoid another potentially devastating blow to their health.